THE INFLUENCE OF ‛MAXIMUM INDICATED SLOPE` AND `TOTAL

THE INFLUENCE OF ‛MAXIMUM INDICATED SLOPE’ AND ‘TOTAL
INDICATED RUN-OUT' ON THE NOISE CAUSED BY THE INTERACTION
OF CONVEYOR IDLER ROLLS AND CONVEYOR BELTS
1
Paul Munzenberger and Craig Wheeler
2
1
TUNRA Bulk Solids Research Associates
2
The University of Newcastle, Australia
ABSTRACT
This paper aims to assess the noise level produced by the interaction of a conveyor belt and
a set of specially machined conveyor idler rolls and then compare it to the standard conveyor
idler roll measurements ‘maximum indicated slope’ (MIS), and ’total indicated run-out’ (TIR).
The findings indicated that a conveyor idler roll’s MIS is the primary influence of the noise
produced by the conveyor idler roll and conveyor belt contact.
1. INTRODUCTION
The noise produced by conveyors is becoming an increasingly important consideration to
their designers and operators, especially when the conveyor or conveyor system is located in
a populated area, as is the case with many ship loading terminals. When designing and
operating a conveyor it is important to know in advance what the likely noise performance of
its components will be so that the design specifications set for the system are not too low –
leading to the purchase of unacceptable components, or too high – leading to components
that are overly expensive.
One of the key noise producers of a conveyor system is its conveyor idler rolls. The noise
produced by conveyor idler rolls can fall into two distinct categories. The first – commonly
known as ’self-noise’ – is the noise produced by the conveyor idler roll’s bearings and seals,
and has been shown to be an insignificant contributor to conveyor noise production [1]. The
second noise category includes the sounds generated by the conveyor idler roll’s interaction
with the rubber conveyor belt that rolls upon it. It is the second noise category that is the
subject of this paper.
The noise produced by the conveyor idler roll’s interaction with the conveyor belt is caused
either by defects in the conveyor belt’s surface or defects on the surface of the conveyor idler
roll’s shell. Previous testing at The University of Newcastle has shown that of these two noise
causes, noises caused by conveyor idler roll shell defects are usually the greater contributor
to the overall noise production. The two main measurements used by industry to determine
the quality of conveyor idler roll shells are ’total indicated run-out’ (TIR) and ‘maximum
indicated slope’ (MIS), but it is not known if there is a correlation between these two
measurements and the noise produced by the conveyor belt and conveyor idler roll
interaction. Throughout this paper the terms ‘total indicated run-out’ and ‘maximum indicated
slope’ will be used frequently, and will be referred to as TIR and MIS respectively.
To determine the extent of noise produced by conveyor idler roll shell defects, two sets of
purposely machined conveyor idler rolls were used. The first group of conveyor idler rolls
were machined with progressively more eccentric shells which provide a group of conveyor
idler rolls with a large TIR, but a small MIS. For this report, these conveyor idler rolls are
known as ’TIR’ conveyor idler rolls. The second group of conveyor idler rolls were machined
true but have a progressively deepening flat machined on their surface which provides a set
of conveyor idler rolls that have a large MIS, but a small TIR. For this report, these conveyor
idler rolls will be known as ’MIS’ conveyor idler rolls. These two groups of conveyor idler rolls
are used to determine if there is a correlation between TIR or MIS and noise output.
It is hoped that this research will aid conveyor system designers with defining appropriate
specifications for conveyor idler rolls so that they will be suitable for the environment in which
they are to operate and are better able to meet budgetary constraints.
B16-02 page 1
2. MEASUREMENTS
2.1 TIR and MIS
TIR is effectively the difference between the largest and smallest radii measured on a single
annular path on the surface of a cylindrical object like a conveyor idler roll. The TIR of a
conveyor idler roll is measured by rotating its shell while its shaft is held stationary, and
reading measurements from a dial indicator or some type of displacement transducer that is
resting on the revolving shell; Figure 1 shows a typical setup. Measurements are taken from
near each end and from the centre of each conveyor idler roll that is tested. Since conveyor
idler rolls are generally round, the largest and smallest radii are usually opposite each other,
however, some surface defects can influence their relative position. It should be noted that
the eccentricity of a conveyor idler roll is not the same as the TIR. In general, the TIR of a
given conveyor idler will be approximately double its eccentricity.
Idler Rotation
Figure 1. MIS and TIR measurements with a linear transducer
The MIS measurement was first proposed by Brown [1]. MIS is measured in the same
manner as the TIR, with the same equipment, and the two are measured together. But unlike
TIR – which is the difference between the largest and smallest radii around a conveyor idler
roll – the MIS is the change in radius for every six degrees around the conveyor idler roll
circumference for a total of 60 separate measurements from which the largest is chosen and
reported as the MIS for that section of conveyor idler roll (hence the word ’maximum’ in MIS).
Since the MIS measurements require a large amount of data, they are always done with a
displacement transducer or laser sensor that measures the conveyor idler roll while it is being
rotated at a constant velocity, and a data acquisition system.
In reality, it is difficult to measure exactly 60 separate points around a conveyor idler roll,
instead, a larger number of points are collected and then the 60 points are found by
interpolation. The interpolation results from one end of an ’as supplied’ conveyor idler roll are
shown in Figure 2; in the results, the smallest measured radius is zeroed and the TIR is then
the range of the data – 0.36 mm in this case – and the MIS is the largest step in the data as
shown – 0.11 mm in this case. Normally the TIR and MIS results for a conveyor idler roll are
given separately for each of the three measurement locations, however in this paper, the
average TIR and MIS of all of the measurements from each conveyor idler roll type is used
instead, since we are considering the noise production of a group of idlers rather than from
individual segments.
B16-02 page 2
Δ Radius (mm)
0.4
0.35
0.3
0.25
0.2
0.15
0.1
0.05
0
MIS
TIR
0
60
120
180
240
300
360
Angle (°)
Figure 2. TIR and MIS data from an ‘as supplied’ conveyor idler roll
2.2 Noise
Sound or noise levels can be measured in three ways: sound pressure, sound intensity, and
sound power. The instrument used to gather the sound data shown in this report measures
sound pressure. However, even though sound pressure is being measured, the results are
not given in linear pascals since the ear responds approximately logarithmically to energy
input, which is proportional to the square of the sound pressure [2]. This means that when
the sound pressure is say, doubled, the listener will not think that they are hearing double the
sound but will hear a much smaller increase. In order to convert the linear pressure
measurements to something that matches what people experience, Equation 1 is used and
the results are reported as decibels rather than pascals.
(
)
(1)
In the equation
is the reported sound level in decibels,
is the measured pressure in
pascals, and
is the reference pressure which has a value of 20 µPa. The reference
pressure is the lowest pressure that the average undamaged human ear is able to detect [2].
Finding the logarithm of a pressure ratio means that the quietest sound that can be heard by
the average person gives a value of 0 decibels; however, quieter sounds can be measured.
The square of the pressure ratio and the log of the square of the pressure ratio are the result
of the quote from the last paragraph. Multiplying everything by ten spreads the data over a
more readable range and also gives rise to the deci in decibels. It is worth noting that when
for the difference in sound pressures of
and
is investigated, it will be found that
dB, thus the sound pressure doubles every
dB. All the graphs in this
paper that depict decibels will have a y-axis divided into multiples of six to approximate the
doubling of the sound level.
Sound measurements are rarely reported without some type of filtering. The aim of the
filtering is to apply more weighting to frequency levels that humans are more sensitive to,
while suppressing other frequencies to which humans have less sensitivity. In Australia most
sound level monitoring is done using the A-weighting noise filter and sound is reported in
dBA. The A-weighting curve for the various frequency bands is given in Figure 3. The
filtering is done by the sound level meter in real time while the sound levels are being
measured.
B16-02 page 3
Figure 3. Various standard frequency weightings that can be
applied to sound measurements [2]
Post processing of the results primarily involves determining the Leq for sound level data
obtained for each test. The Leq is the equivalent continuous sound pressure level [2] or steady
sound that is equivalent to an extended period of time-varying sound level measurements on
a time averaged basis. All of the sound level results presented here are Leq values
determined from sound level measurements of between 30 and 50 seconds duration.
Finally, while measuring the noise level of the test conveyor idler rolls, the background noise which includes the ambient noise and the noise of the conveyor itself - was also measured.
Since the noise of the conveyor and the conveyor idler rolls are incoherent noise, the
background noise can be subtracted from the conveyor idler roll noise with Equation 2.
(
⁄
⁄
)
(2)
Where is the noise of the conveyor idlers by themselves, and
and
are the combined
noise and the background noise respectively. This equation subtracts incoherent sounds on
a linear energy (pressure squared) basis [2] and cannot be used if the difference between the
total noise and the background noise is less than 3 dB.
3. TEST INSTRUMENTS
The two principle instruments that were used during the testing were the sound level meter
shown in Figure 4 and the weather meter shown in Figure 6. Details of each instrument can
be found in Error! Reference source not found. and Error! Reference source not found..
B16-02 page 4
Figure 4. Sound level meter
Figure 5. 94 dB reference for the sound level meter
Instrument Type
Make
Model
Serial Number
Class
Sound Level Meter (SLM)
01dB
SLS95S
30520
2
Table 1. Sound level meter data
B16-02 page 5
Figure 6. Weather meter
Figure 7. Weather meter and weather vane
Instrument Type
Make
Model
Serial Number
Pocket Weather Tracker
Kestrel
4500
3565900
Table 2. Weather meter data
B16-02 page 6
4. CONVEYOR IDLER ROLL NOISE TEST RIG
The test rig used for the sound pressure level testing is shown in
Figure 8 and Figure 9. It was designed to be mounted on the flat return side of a conveyor
with a 600 mm wide conveyor belt. It consists of five equally spaced mounting points for the
test conveyor idler rolls, with three mounts located above the belt, and the remainder on a
separate frame below the belt (Figure 9). The distance between the upper and lower
conveyor idler rolls can be varied to alter the wrap angle (the contact angle between the belt
and the conveyor idler roll). The zigzag path is designed to apply a load to the test idler rolls
without the use of bulk material. The test rig is also mounted on its own heavy mounting
structure which does not contact the test conveyor structure. The only modification made to
the host conveyor was the removal of the trough and return conveyor idler rolls and their
frames in the vicinity of the test rig in order to reduce the background noise.
Figure 8. Conveyor idler roll noise test rig
The belt used on the conveyor is a 2-ply polyester nylon (PN) fabric reinforced belt that has a
nominal thickness of 6 mm. The use of such a light belt for this type of noise testing is
thought to be advantageous since its light weight enables it to be accelerated quickly by
conveyor idler roll defects – thereby increasing the noise output; and the light weight belt is
freer to vibrate – enabling it to transmit more noise with less damping.
Figure 9. Zigzag path of conveyor belt through test rig
B16-02 page 7
5. TEST CONVEYOR IDLER ROLLS
All the testing was conducted with a set of 20 plain conveyor idler rolls specifically purchased
for the testing. The conveyor idler rolls featured standard steel shells with a nominal overall
diameter of 152 mm, a shell length of 650 mm, and were of the Garland type.
Initially five idlers were randomly selected to test in the ’as supplied’ condition; after testing,
these were then turned in the lathe along with the other 15 idlers in four groups of five idlers
with each group of idlers given a different offset. The turning operation is shown in Figure 10.
The turning was done between centres with special adaptors to provide the desired offset.
During the turning operation the shell is fixed to the shaft by the piece of angle (welded to the
shell) and threaded rod on the left hand end so that there cannot be any relative motion
between the two. The turning operation produced four sets of conveyor idler rolls with a
varying TIR and a small MIS. These conveyor idler rolls are known as TIR conveyor idler
rolls. All of the conveyor idler rolls have finished shell diameters of between 150 and 150.5
mm.
Figure 10. Turning a conveyor idler roll between centres
Once the four sets of offset conveyor idler rolls were tested, the set of five conveyor idler rolls
labelled as concentric were returned to the workshop to have a small flat machined on each
one as shown in Figure 11. The modified set of conveyor idler rolls were tested again then
returned to the workshop to have their flats made larger. In all, three flat depths were tested
on these conveyor idler rolls. Additionally, the set of five conveyor idler rolls labelled as 0.50
mm TIR were also tested again after they had had a 0.05 mm deep flat machined on their
shells. The milling operation produced four sets of conveyor idler rolls with a varying MIS and
a small TIR. These conveyor idler rolls are known as MIS conveyor idler rolls.
Figure 11. Milling a flat on a conveyor idler roll
The desired TIR and flat depths for the conveyor idler rolls are shown in Table 3. How the
dimensions are measured is shown in Figure 12. Note that the dimension ’A’ is not the TIR
B16-02 page 8
measurement, and should be doubled to be equivalent to the TIR. Alongside the desired
dimensions for the offsets and flats in Table 3 are the actual average measured dimensions.
Unfortunately there is some difference between the desired and actual measurements but this
did not affect the final results.
Figure 12. Diagrams showing A - shell offset, and B - flat depth
TIR Conveyor Idler Rolls
Desired TIR - 2A
Actual TIR - 2A
(mm)
(mm)
MIS Conveyor Idler Rolls
Desired Flat Depth
Actual Flat Depth
B (mm)
B (mm)
0.00
0.24
0.05
0.088
0.50
0.51
0.10
0.152
0.75
0.80
0.15
0.220
1.00
1.00
0.20
0.288
Table 3. Actual offset and flat measurements
6. TEST AREA
A diagram of the area in which the sound testing was conducted is shown in Figure 13. The
location of the sound level meter is shown in Figure 14, and the ground conditions during the
testing can be seen in
Figure 8. The sound level meter was placed on a tripod as near as possible to the conveyor
idler rolls whose noise output was being tested.
B16-02 page 9
Figure 13. Sound testing area
Figure 14. Sound level meter location.
7. TEST PROCEDURE
For each noise level test, five conveyor idler rolls were installed in the test frame and the test
frame was adjusted so that the wrap angle was 10°. The weather meter was set up nearby
and set to record air temperature, air pressure, humidity, wind speed, and wind direction, and
the sound level meter was set up in the position shown and set to record. The sound level
meter was set to measure dBA with a ‘fast’ time constant and a sample rate of 32 times per
second. The noise level was recorded for each conveyor speed from 0 m/s to 6 m/s then
immediately from 6 m/s to 0 m/s in steps of 1 m/s for a period of one minute per step. The
weather and sound level data were then downloaded to a computer for analysis.
In all, ten separate noise level tests were conducted. Four sound level tests on four sets of
five TIR conveyor idler rolls, four noise level tests on four sets of five MIS conveyor idler rolls,
one noise level test on a set of ’as supplied’ conveyor idler rolls, and a noise level test for
which the test frame had no conveyor idler rolls in it at all in order to determine the
background noise of the conveyor system. The background noise of the conveyor was only
tested on two occasions early in the testing as it is known that the noise output of the
conveyor system does not change significantly, especially at higher speeds. All testing was
conducted at night time when the background noise was at a minimum.
From each group of machined conveyor idler rolls, two were selected to have their TIR and
MIS measured. From the group of ’as supplied’ conveyor idler rolls, three were selected.
When a group of idlers was re-machined, the same two conveyor idler rolls that were
measured before they were modified were used to find the TIR and the MIS of the new set.
All reported TIR and MIS measurements are the average of the six or nine measurements
taken for each set of conveyor idler rolls.
B16-02 page 10
8. RESULTS
8.1 Raw Noise and Weather Data
Figure 15 shows a typical set of conveyor idler roll noise results copied from the analysis
software; the graph shows the results for the set of idlers with a 0.1 deep flat machined on
their shells. The seven steps of the noise results graph represent the noise measured for
each velocity of the conveyor from 0 m/s to 6 m/s in 1 m/s steps. The two vertical lines on the
graph are used to determine the Leq for the section between them. The Leq is the time
averaged sound pressure level of the data in the time period between the cursors, as
explained in section 2.2. The cursors were moved over each step in the graph to determine
the Leq for that velocity. The software used does not display the units for the graph axes, but
the vertical axis is in units of dBA, and the horizontal axis is in units of hours and minutes.
Figure 15. Typical noise test results
Three graphs showing the weather data that was typical for all of the tests are shown in
Figure 16. Only air temperature, humidity and air pressure (absolute) are shown. Wind
speed and direction were recorded for all tests but since there was virtually no wind recorded
there is no need to present that data here.
Figure 16. Typical weather data
B16-02 page 11
8.2 TIR and MIS Data
The averaged TIR and MIS measurements for the nine sets of conveyor idler rolls are given in
Table 4. The TIR and MIS data was taken from results similar to and including those graphed
in Figure 2 and Figure 17 (note the rough surface measurements of the ’as supplied’
conveyor idler roll in Figure 2 compared to smooth surface measurements of the machined
TIR conveyor idler roll in Figure 17). The measurements of the ’as supplied’ conveyor idler
rolls are shown under the ’TIR Conveyor Idler Rolls’ column. The MIS measurements for the
MIS conveyor idler roll sets were done by hand with a dial indicator measuring the difference
from the edge of the flat to the lowest point of the flat. This was done because it was found
that the measuring equipment that was available was inadequate to measure such large
defects. Also, the TIR measurements for the MIS conveyor idler roll sets do not include the
influence of the flat – which in some cases would have doubled the TIR measurement.
TIR Conveyor Idler Rolls
TIR
MIS
Group
(mm)
(mm)
MIS Conveyor Idler Rolls
TIR
MIS
Group
(mm)
(mm)
0.00
0.24
0.019
0.050
0.57
0.088
0.50
0.51
0.035
0.100
0.24
0.152
0.75
0.80
0.049
0.150
0.24
0.220
1.00
1.00
0.062
0.200
0.25
0.288
As Sup.
0.49
0.093
Table 4. Conveyor idler roll TIR and MIS
Run Out (mm)
0.6
0.5
0.4
0.3
0.2
0.1
0
0
60
120
180
240
300
360
Angle (°)
Figure 17. TIR and MIS data for a 0.5 mm offset TIR conveyor idler roll
8.3 Collated Noise Data
The overall combined noise data is graphed in Figure 18. The data in the graph can be
divided into three groups. The upper group includes five lines of data and is the noise levels
caused by the four MIS conveyor idler roll sets as well as the ’as supplied’ conveyor idler rolls.
The middle group has four lines of data in it and is the noise generated by the four TIR
conveyor idler roll sets. The final group is the lowest line of data shown. This is the
background noise of the conveyor with no conveyor idler rolls installed in the test rig.
When the results from Figure 18 are separated into TIR and MIS conveyor idler roll groups,
Figure 19 and Figure 20 are the respective results. These two graphs are the main goal of
this research and clearly show the influence of TIR and MIS on noise production for 3, 4, 5,
and 6 m/s belt speed. Figure 21 shows a section of the graph from Figure 20 with the data
points from the ’as supplied’ conveyor idler rolls added.
B16-02 page 12
Leq (dBA)
The graphs in Figure 18 to Figure 21 all show ’overall’ noise levels. If Equation 2 is used to
subtract the background conveyor noise from the these results to determine the noise levels
attributed to the sets of test conveyor idler rolls, it is found that there is very little difference
between test conveyor idler roll noise and the overall noise. This is primarily due to the
relatively large difference between the two measurements (remember that dBA is graphed on
a log10 basis), and the close proximity of the sound level meter to the noise source of interest.
102
96
90
84
78
72
66
60
54
48
42
36
0.20 MIS
0.15 MIS
0.10 MIS
As Supplied
0.05 MIS
1.00 TIR
0.75 TIR
0.50 TIR
0
2
4
6
Conveyor Velocity (m/s)
0.00 TIR
No Idlers
Figure 18. Combined conveyor idler roll noise data
102
Leq (dBA)
90
78
6 m/s
66
5 m/s
54
4 m/s
3 m/s
42
0.00
0.50
1.00
1.50
Average TIR (mm)
Figure 19. Noise results for TIR conveyor idler rolls
102
Leq (dBA)
90
78
6 m/s
66
5 m/s
54
4 m/s
42
0.000
3 m/s
0.100
0.200
0.300
0.400
Average MIS (mm)
Figure 20. Noise results for MIS conveyor idler rolls
B16-02 page 13
6 m/s
Leq (dBA)
90
5 m/s
4 m/s
78
3 m/s
As Supplied 6m/s
As Supplied 5 m/s
66
0.088
0.098
Average MIS (mm)
As Supplied 4 m/s
As Supplied 3 m/s
Figure 21. ’As supplied’ conveyor idler roll noise results compared with MIS conveyor idler
roll data
9. DISCUSSION
9.1 TIR Effects on Conveyor Idler Roll Noise Production
The results graphed in Figure 19 clearly show that as the TIR of otherwise perfect idlers is
increased, there is no obvious increase in their noise output due to their interaction with a
conveyor belt. However this statement ignores two key points. Firstly, if a conveyor idler roll
with a large TIR is rotating fast enough, there is a chance that its profile could accelerate
away from the conveyor belt that is riding upon it at a speed that is faster than the
acceleration of gravity. This speed difference would cause the idler surface to fall away from
the belt and subsequently rise to contact it again, most likely with considerable force. The
repeated impact that would result would probably be unacceptably noisy. Secondly, it can be
seen in
Figure 8 that there is cross bracing on the front and back of the test rig. This cross bracing
was added to prevent the test rig from shaking violently when the TIR conveyor idler rolls
were being tested. On a conveyor, conveyor idler rolls with a large TIR would shake the
conveyors structure enough to cause its components to become loose over time which would
allow them to vibrate against each other and thereby create a significant level of noise.
9.2 MIS Effects on Conveyor Idler Roll Noise Production
The results graphed in Figure 20 clearly show that as the MIS of a conveyor idler roll
increases so does its noise output due to its interaction with a conveyor belt, in fact, the noise
output is nearly doubled for an increase in MIS of 0.2 mm in the range tested. When the
noise output of the ’as supplied’ conveyor idler rolls is compared with their average MIS, there
is a very close correlation with the results from the MIS conveyor idler rolls as shown in Figure
21.
It is also worth noting that results for the conveyor idler rolls with an MIS of 0.088 mm match
closely with the trends of the other MIS data points even though this set of conveyor idler rolls
have a TIR that is around double that of the other sets of MIS conveyor idler rolls, this is also
true of the ’as supplied’ conveyor idler rolls. This would tend to indicate that the TIR of a
group of conveyor idler rolls has little effect on their noise output whilst they are interacting
with a conveyor belt.
9.3 Combined TIR and MIS Results
To combine the noise output results from Figure 19 and Figure 20 it must first be recognised
that it is impossible to have a conveyor idler roll that has a TIR of 0 mm and some greater
value for its MIS, and that the opposite is also true. Therefore, for a conveyor idler roll to
have 0 mm TIR, than it must also have an MIS of 0 mm. Now, if the four data sets from
Figure 19 are extrapolated to 0 mm TIR and the average of the data sets used as the values
at zero, this is reasonable since they form very nearly horizontal lines, we have the noise
output of a perfectly concentric conveyor idler roll set, or a conveyor idler roll set with a TIR of
B16-02 page 14
0 mm. This perfect conveyor idler roll set must, as we have pointed out, have an MIS of 0 mm
as well, and when these new data points are added to Figure 20, the result in Figure 22
shows that there is reasonable agreement with the new data points at 0 mm MIS and the rest
of the graph.
9.4 Belt Noise
The topic of belt noise production is outside the scope of this paper, but it is very closely
related and there were some interesting points found during testing that are well worth noting
here. It was found during the testing that when the TIR conveyor idler rolls were tested the
noise level would periodically fluctuate as in Figure 23, which shows the noise measurements
for an offset conveyor idler roll running at 6 m/s. As in Figure 15, the vertical axis is in units of
dBA and the horizontal axis is in units of minutes and seconds. These fluctuations are in
contrast to the steady noise level that was recorded for a flat conveyor idler roll as shown in
Figure 15. The two cursors in Figure 23 are aligned over the fluctuations to show their period
which turns out to be 22.875 seconds as indicated. The belt length is 136.5 m and at a speed
of 6 m/s it cycles through the system in 22.75 seconds; which, given some error in the
measurements, is comparable to the period recorded by the sound level meter. The similarity
of these two results indicates that the noise level fluctuations are caused by the belt and its
surface imperfections.
102
Leq (dBA)
90
78
6 m/s
66
5 m/s
54
4 m/s
3 m/s
42
0
0.1
0.2
0.3
0.4
Average MIS (mm)
Figure 22. 0 mm MIS data added to Figure 20
Time – 22.875s
Figure 23. Noise fluctuations due the conveyor belt
It is likely that the periodical spikes in the noise level are caused by belt surface defects like a
splice or the marks shown in Figure 24 which is a photograph of a defect on the surface of the
test conveyor’s belt. Each set of TIR conveyor idler roll noise level data showed the same
pattern. It is thought that since the TIR conveyor idler rolls all had smooth, round machined
B16-02 page 15
shells, they were unable to generate any noise and that the noise levels measured for the TIR
conveyor idler rolls are entirely due to the belt, since the measured noise levels are roughly
constant for each speed regardless of the TIR.
The conditions required to get a noise pattern like that shown in Figure 23 are fairly specific
and are easily disrupted by a defect such as the flats machined on the MIS conveyor idler
rolls or the surface of the ’as supplied’ conveyor idler rolls. It is likely then that the noise level
attributed to the belt is the lower limit that can be expected when testing for conveyor idler roll
noise. It is recommended that any comprehensive noise testing of conveyor idler rolls be
conducted so that it may be determined if the conveyor belt is the primary influence on the
overall noise production. This may prevent resources from being wasted on an effort to
produce the impossibility of quieter conveyor idler rolls.
Figure 24. One cause of the noise fluctuations
10. CONCLUSION
The results shown indicate that the MIS of a conveyor idler roll is the dominant cause of the
noise produced by the interaction of a conveyor idler roll and the conveyor belt that is in
contact with it. They also show that the TIR of a conveyor idler roll has very little to do with
the same noise production. This does not mean however, that the TIR is a redundant
measurement. The TIR measurement will give an indication of the balancing of a conveyor
idler roll which, if poor, can lead to the severe vibrations that were witnessed for the TIR
conveyor idler rolls during the testing.
The testing also found that it was possible to measure the noise caused by the conveyor belt
due to its interaction with conveyor idler rolls, and that if this pattern was found during testing
for conveyor idler roll noise, then the conveyor idler rolls will be operating as quietly as is
possible. It is recommended that further research be conducted into this area of conveyor
system noise production.
B16-02 page 16
REFERENCES
[1]
[2]
Brown S. C., Conveyor Noise Specification and Control, Acoustics 2004.
Bies and Hansen, Engineering Noise Control: Theory and Practice, Taylor & Francis
2009 (Electronic Edition).
ABOUT THE AUTHORS
MR PAUL MUNZENBERGER
Paul Munzenberger completed an apprenticeship as a Fitter Machinist in early 2001, and
spent several years afterwards as a tradesman principally involved with maintenance and
repair of ’Cable Belt’ and conventional trough conveyors, as well as a variety of other
equipment associated with coal handling and preparation. He completed his Bachelor’s
Degree in Mechanical Engineering at the University of Newcastle in 2007 with first class
honours. He is currently studying part-time for a PhD in Mechanical Engineering in the field of
belt conveying technology, while working as a Research Engineer for TUNRA Bulk Solids.
Mr Paul Munzenberger
TUNRA Bulk Solids Research Associates
The University of Newcastle
University Drive
Callaghan NSW 2308 AUSTRALIA
Telephone: (+61 2) 403 39012
Email:
[email protected]
DR CRAIG WHEELER
Craig Wheeler is a Senior Lecturer in the School of Engineering at The University of
Newcastle, Australia and Associate Director of TUNRA Bulk Solids. He worked as a
Mechanical Engineer for BHP Billiton for eleven years and then as a Research Fellow at the
Centre for Bulk Solids and Particulate Technologies for four years. He was appointed as a
Lecturer in Mechanical Engineering in 2002, as a Senior Lecturer in 2008 and more recently
as Associate Director of TUNRA Bulk Solids.
Dr Craig Wheeler
Discipline of Mechanical Engineering
School of Engineering
The University of Newcastle
University Drive
Callaghan NSW 2308 AUSTRALIA
Telephone: (+61 2) 403 39037
Email:
[email protected]
B16-02 page 17